Method for manufacturing a cylinder for internal combustion engine

ABSTRACT

A method is provided for manufacturing a cylinder for an internal combustion engine, which makes it possible not only to manufacture the cylinder by a high-pressure die casting method at low cost and in high precision, but also to prevent relative misalignment among the scavenging port, suction port and exhaust port of the cylinder. This method is characterized by the steps of: preparing a cylinder liner made of an aluminum alloy pipe and provided with the scavenging port, and a bore-core die as well as cores for scavenging ducts both being uncollapsible and configured so as not to intrude into the scavenging ports; setting the cylinder liner in place in the bore-core die; and casting, by means of metal mold casting method, an aluminum alloy onto the outer peripheral surface of the cylinder liner to thereby mold a main body of the cylinder.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for manufacturing a cylinder for an internal combustion engine such as a small air-cooled two-stroke gasoline engine. In particular, the present invention relates to a manufacturing method of the cylinder for an internal combustion engine to be used, for example, in a portable power working machine, the manufacturing method enabling an undercut portion of the cylinder such as a scavenging port to be rationally formed in the manufacture of the cylinder by means of a die casting method such as a high-pressure die casting method.

[0003] 2. Description of the Related Art

[0004] The cylinder of a small air-cooled two-stroke gasoline engine to be used in a portable power working machine is, as seen for instance from JP Laid-open Patent Publication (Kokai) No. 58-155114 (1983), generally formed of an aluminum alloy and constituted by an integral body consisting of a main body having a cylinder bore formed therein for allowing a piston to be fitted therein, and a head portion having a squish dome-shaped combustion chamber formed therein, and by a large number of cooling fins projecting from all over the outer wall of the integral body.

[0005] The cylinder bore is provided with a suction port and also with an exhaust port, both of which are designed to be closed or opened by the movement of the piston, these suction port and exhaust port being arranged so as to face each other in an off-set manner so that they differ in level from each other. A plurality of hollow scavenging ducts, each being displaced away from these suction port and exhaust port by an angle of 90 degrees and having an inner wall of predetermined thickness, are formed along with the cylinder bore. The downstream end portion (upper end portion) of each hollow scavenging duct is constituted by a scavenging port, thereby providing a pair of scavenging ports which are disposed opposite to each other and designed to be opened and closed by the piston, these scavenging ports being inclined somewhat upward and directed in the direction opposite to the exhaust port of the cylinder bore.

[0006] The cylinder disclosed in the aforementioned JP Laid-open Patent Publication (Kokai) No. 58-155114 is a so-called binary fluid scavenging type cylinder where a pair of scavenging ports are symmetrically formed with respect to the longitudinal section taken along the middle of the exhaust port. Additionally, a so-called quaternary fluid scavenging type cylinder where a pair of scavenging ports are additionally provided therewith (two pairs of scavenging ports in total) is also known.

[0007] As for the type of the scavenging duct, there are known a hollow scavenging duct provided with an inner wall as shown in the aforementioned JP Laid-open Patent Publication (Kokai) No. 58-155114, a scavenging duct having no inner wall (the side facing the cylinder bore is opened), and, as shown in the aforementioned JP Laid-open Patent Publication (Kokai) No. 2000-34927, a scavenging duct provided with a half-wall and featured in that it is provided at a lower portion thereof with an opening extending in the longitudinal direction of the scavenging duct while leaving a half-wall having a predetermined thickness at an upper portion thereof so as to allow an air-fuel mixture introduced through the scavenging duct into the scavenging port from the crank chamber to be directly contacted with a skirt portion of the piston.

[0008] In the manufacture of a cylinder provided with an inner wall-attached (or a half-wall-attached) hollow scavenging duct, in particular among the aforementioned cylinders for a two-stroke internal combustion engine, by means of a die casting method such as a high-pressure die casting method which enables the cast molding of high dimensional precision at low cost, the scavenging port portion of the scavenging duct which constitutes an undercut portion has been generally created by the following procedures. Namely, since a collapsible core for forming the cylinder bore portion cannot be employed under a high pressure, a raw cylinder body is cast-molded at first in such a manner that the scavenging port portion (constituting an undercut portion) thereof is left closed, and thereafter, this closed scavenging port portion is cut out by mechanical means (see JP Laid-open Patent Publication (Kokai) No. 58-155114 (1983)).

[0009] There is a problem however in the aforementioned method to cut out a scavenging port by mechanical means after the casting of raw cylinder body. Namely, since the space for allowing a cutting tool to be inserted into a working portion is very narrow, it is very difficult to perform the mechanical working and to enhance the processing accuracy of the scavenging port. In this case, since the performance of a two-stroke internal combustion engine is greatly influenced by the size and configuration of the scavenging port as well as by the processing accuracy thereof, this problem associated with the aforementioned mechanical working is very important.

[0010] It may be conceivable to manufacture a cylinder provided with an inner wall-attached hollow scavenging duct by means of a die casting method employing an insert core to be inserted into the scavenging port portion. In this case however, since part of the insert core is left in the cast product, the heat conductivity thereof is deteriorated and at the same time, various problems such as the deformation or peeling due to the remaining insert core may occur.

[0011] Meanwhile, as for the manufacturing method of a cylinder for an internal combustion engine, there is also known, as described above in JP Patent Publication No. 52-47091 (1977) and JP Laid-open Patent Publication (Kokai) No. 1-309774 (1989), a method wherein a cylinder liner (sleeve) provided in advance with a scavenging port, a suction port and an exhaust port is manufactured (cast) at first by making use of a ferrous material, and then, a main body of cylinder is cast by means of metal mold casting on the outer peripheral surface of the cylinder liner by making use of an aluminum alloy as a raw material.

[0012] However, the cylinders that can be manufactured by the methods shown in JP Patent Publication No. 52-47091 and JP Laid-open Patent Publication No. 1-309774 are accompanied with problems that since the cylinder liner portion is formed of a ferric cast article, a mold which is exclusively designed for the manufacture of the cylinder liner portion is required to be separately prepared thus resulting in an increase of manufacturing cost, and that since the cylinder liner is formed of a material which differs in thermal expansion coefficient as well as in thermal conductivity from those of the material from which the main body of the cylinder is formed, there are significant possibilities of generating problems such as peeling between them, a step portion around the opening such as scavenging port or misalignment between them.

[0013] Further, according to the manufacturing method described in JP Patent Publication No. 52-47091, the scavenging port portion, suction port portion and exhaust port portion of the cylinder liner are all constructed so as to protrude outward from the cylindrical portion of the cylinder liner in order to prevent a melt from entering into the interior (through opened portions) of the cylinder liner on the occasion of the casting the main body of the cylinder, so that a mold, an insert core, etc. each having a complicated configuration, are required to be employed, thereby further increasing the manufacturing cost of the cylinder.

[0014] On the other hand, according to the manufacturing method described in JP Laid-open Patent Publication No. 1-309774, since it is required to employ a collapsible core as insert cores for forming a bore-core die, each of the openings and each of the ducts, it is impossible to apply this manufacturing method to the manufacture of the cylinder by making use of a die casting method such as a high-pressure die casting method which enables the cast molding of high dimensional precision at low cost.

BRIEF SUMMARY OF THE INVENTION

[0015] The present invention has been made to overcome the aforementioned problems accompanied with the prior art, and therefore an object of the present invention is to provide a method for manufacturing a cylinder for an internal combustion engine, which not only makes it possible to manufacture the cylinder by means of a die casting method such as a high-pressure die casting method at low cost and in high precision without raising problems such as the deterioration of heat conductivity, and the deformation or peeling of the cylinder, but also makes it possible to prevent relative misalignment among the scavenging port, the suction port and the exhaust port of the cylinder to be obtained.

[0016] With a view to realize the aforementioned object, the present invention provides a manufacturing method of a cylinder for an internal combustion engine provided with an inner wall-attached hollow scavenging duct having a scavenging port to be opened and closed by the movement of a piston, the method being characterized by the steps of: preparing a cylinder liner made of an aluminum alloy pipe and provided with the scavenging port, and a bore-core die as well as a core for scavenging duct both being uncollapsible and configured so as not to intrude into the scavenging port; setting the cylinder liner in place in the bore-core die; and casting, by means of metal mold casting method, an aluminum alloy as a raw material onto the outer peripheral surface of the cylinder liner to thereby mold a main body of the cylinder.

[0017] In a preferable embodiment, the cylinder liner is provided in advance with a suction port as well as an exhaust port in addition to the scavenging port.

[0018] In another preferable embodiment, melt intrusion prevention means is provided for preventing melt from entering into the scavenging port on the occasion of metal mold casting. Preferably, the melt intrusion prevention means is designed so as to prevent the generation of a step portion between the scavenging port and the scavenging duct of the main body of cylinder. As a preferable embodiment of the melt intrusion prevention means, a blocking member is employed and removably attached to the scavenging port.

[0019] As another preferable embodiment of the melt intrusion prevention means, a thick-walled portion or a rib portion to be face-contacted with the core for the scavenging duct is provided around an outer periphery of the cylinder liner excluding a lower side of the scavenging port in a manner to prevent the generation of a step portion relative to the scavenging port.

[0020] In a preferable embodiment, a chamfered portion is formed in advance on an inner periphery of an opening such as the scavenging port formed in the cylinder liner.

[0021] In another preferable embodiment, a portion of the outer peripheral surface of the cylinder liner, which contacts with the main body of the cylinder, is coated in advance with a metal having a lower melting point than that of the aluminum alloy.

[0022] According to the aforementioned preferable embodiments of the method of manufacturing a cylinder for an internal combustion engine which is constructed as described above, due to the employment of the die and the insert core both being uncollapsible, it is possible to utilize a high-pressure die casting method which enables one to obtain a cast article of high dimensional precision at low cost. Additionally, since the cylinder liner is provided in advance with a scavenging port, a suction port and an exhaust port, it is possible to manufacture the cylinder with higher precision and at lower cost as compared with the conventional manufacturing methods such as the method wherein the port portions such as the scavenging port are cut out by mechanical working after die casting or the method wherein an insert core to be inserted into the scavenging port portion is used. At the same time, it is now possible to obviate the aforementioned problems of the deterioration of heat conductivity as well as the deformation or peeling of these port portions due to the remnant of the insert core in the cast article (cylinder).

[0023] Additionally, since the cylinder liner is formed by making use of an aluminum alloy pipe, the cylinder liner can be manufactured at a lower cost as compared with the case where a liner produced through casting is employed. Further, since the cylinder liner is formed of the same material (aluminum alloy) as that of the main body of the cylinder, there is no possibility of generating any difference in thermal expansion coefficient as well as in thermal conductivity, thereby making it possible to inhibit the generation of problems such as peeling between them, a step portion around the opening such as scavenging port or misalignment between them. Further, since the cylinder liner and the main body of the cylinder are formed of the same material with each other, it is advantageous in terms of recycle (re-use) of materials.

[0024] Furthermore, since the cylinder liner is provided in advance with these scavenging port portion, suction port portion and exhaust port portion, there is little possibility of generating relative misalignment among these port portions, thus uniquely determining the positions of the scavenging port, the suction port and the exhaust port, thereby making it possible to obtain the cylinder excellent in dimensional precision and preventing the generation of relative mismatching among the scavenging port, the suction port and the exhaust port with regard to the timing of opening and closing to be effected by the piston.

[0025] Since the melt intrusion prevention means is provided for preventing melt from entering into the scavenging port on the occasion of metal mold casting, it is now possible to reliably prevent the melt from entering into the scavenging port, thus making it possible to save the time and labor required for the finish working of the cylinder such as deflashing work after the casting thereof. Moreover, since the melt intrusion prevention means is designed so as to prevent the generation of a step portion between the scavenging port and the scavenging duct of the main body of the cylinder, it is possible to prevent the generation of turbulence in the scavenging gas flow to be injected in the combustion chamber disposed over the top of piston.

[0026] Further, when the inner peripheral edge portion of the opening such as the scavenging port, etc. that has been formed in advance in the cylinder liner is preliminarily chamfered, finish chamfering work after casting can be easily performed.

[0027] Further, when a specific region in the outer peripheral surface of the cylinder liner, which is designed to be contacted with the main body of the cylinder is coated (through electroplating, nonelectrolytic plating, ion plating, etc.) with a metal (for example, zinc, tin, etc.) having a lower melting point than that of the aluminum alloy, the metal thus coated is enabled to melt on the occasion of casting, resulting in enhancement of adhesion between the cylinder liner and the main body of the cylinder. As a result, the heat conduction from the cylinder liner to the main body of the cylinder can be enhanced, thus improving the heat dissipation and cooling properties of the cylinder.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0028]FIG. 1 is a longitudinal sectional view of the scavenging port portion, as a cylinder liner to be used in one embodiment of the manufacturing method of cylinder for internal combustion engine according to the present invention is set in position in a bore-core die as well as in the core for the scavenging duct;

[0029]FIG. 2 is a longitudinal sectional view of the suction port portion and the exhaust port portion, as a cylinder liner to be used in one embodiment of the manufacturing method of cylinder for internal combustion engine according to the present invention is set in position in a bore-core die as well as in the core for the scavenging duct;

[0030]FIG. 3 is a plan view of the cylinder liner shown in FIGS. 1 and 2;

[0031]FIG. 4 is a longitudinal sectional view of the scavenging port portion for illustrating the metal mold casting in one embodiment of the manufacturing method of cylinder for internal combustion engine according to the present invention;

[0032]FIG. 5 is a longitudinal sectional view of the suction port portion for illustrating the metal mold casting in one embodiment of the manufacturing method of cylinder for internal combustion engine according to the present invention;

[0033]FIG. 6 is an enlarged partial sectional view showing one example of the melt intrusion preventing means which is adapted to be used in one embodiment of the manufacturing method of cylinder for internal combustion engine according to the present invention;

[0034]FIG. 7 is a cross-sectional view taken along the line VII-VII of FIG. 6;

[0035]FIG. 8 is an enlarged partial sectional view showing another example of the melt intrusion preventing means;

[0036]FIG. 9 is a cross-sectional view taken along the line IX-IX of FIG. 8;

[0037]FIG. 10 is a longitudinal sectional view of the scavenging port portion for illustrating the metal mold casting in another embodiment of the manufacturing method of cylinder for internal combustion engine according to the present invention;

[0038]FIG. 11 is a longitudinal sectional view of the scavenging port portion, illustrating the cylinder for a small air-cooled two-stroke gasoline engine, which can be manufactured according to one embodiment of the manufacturing method of the cylinder for the internal combustion engine of the present invention; and

[0039]FIG. 12 is a longitudinal sectional view of the suction port portion, illustrating the cylinder for a small air-cooled two-stroke gasoline engine, which can be manufactured according to one embodiment of the manufacturing method of the cylinder for the internal combustion engine of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention will be further explained with reference to one embodiment of the manufacturing method of a cylinder for an internal combustion engine where an insert core is employed according to the present invention.

[0041] The cylinder for an internal combustion engine, which can be manufactured by the method according to this embodiment, is a cylinder 1 for a small air-cooled two-stroke gasoline engine as shown in FIG. 11 (a longitudinal sectional view wherein the scavenging port thereof is longitudinally sectioned) and FIG. 12 (a longitudinal sectional view wherein the suction port and exhaust port thereof are longitudinally sectioned), the engine being designed to be employed in a portable working machine. This cylinder 1 is constituted by a main body 2A of the cylinder which is made of an aluminum alloy and by a cylinder liner 2B, the inner peripheral surface of which defines a cylinder bore 10. The head portion 3 of the cylinder is provided with a combustion chamber 4 which is squish dome-shaped for instance. The main body 2A of the cylinder is provided, on the outer peripheral surface thereof, with a large number of cooling fins 9 which are formed integral with the main body 2A. Further, the combustion chamber 4 is provided with an ignition plug-mounting hole 23 (in which an internal thread 23 a will be formed after cast molding).

[0042] The cylinder 1 is provided with a suction port 11 and with an exhaust port 12, which are to be closed and opened by the movement of the piston 60, these suction port 11 and exhaust port 12 being disposed to face each other and off-set level-wise from each other. The cylinder 1 is also provided with two pairs of hollow scavenging ducts 14 and 15, each pair being displaced away from these suction port 11 and exhaust port 12 by an angle of 90 degrees (see also FIG. 3). Namely, the cylinder 1 in this case is a so-called quaternary fluid scavenging type cylinder where two pairs of scavenging ports are symmetrically formed with respect to the longitudinal cross-section F taken along the middle of the exhaust port 12. The downstream end portion (upper end portion) of each of the hollow scavenging duct 14 and 15 is constituted by a scavenging port 16 or 17, thereby providing two pairs of scavenging ports 16 and 17 disposed opposite to each other, which are designed to be opened and closed by the movement of the piston 60 and are inclined somewhat upward in the direction opposite to that of the exhaust port 12 (i.e. directed toward the suction port 11) of the cylinder bore 10.

[0043] These paired scavenging ducts 14 and 15 are respectively provided with a half wall. Namely, in order to permit an air-fuel mixture (which is going to be introduced through each of scavenging ducts 14 and 15 into each of the scavenging ports 16 and 17 from the crank chamber (not shown)) to contact with the skirt portion of the piston 60, paired scavenging inlet openings 21 and 22 are formed at a lower portion of the scavenging ducts 14 and 15, respectively, while leaving paired half walls 18 and 19 each having a predetermined thickness (the thickness of the cylinder liner 2B) at an upper portion of the scavenging ducts 14 and 15.

[0044] In the manufacture of the cylinder 1 constructed as described above, the cylinder liner 2B made of an aluminum alloy pipe having a predetermined wall thickness and a predetermined inner diameter and provided with two pairs of scavenging ports 16 and 17, two pairs of scavenging inlet openings 21 and 22, the suction port 11 (the inner end portion 11 a thereof), and the exhaust port 12 (the inner end portion 12 a thereof), all of these openings and ports being formed by a suitable mechanical working; and the bore-core die 50 as well as two pairs of cores 55 and 56 for scavenging ducts (see FIGS. 4 and 5) all being uncollapsible and configured so as not to intrude into the each of paired scavenging ports 16 and 17 as shown in FIGS. 1, 2 and 3 are prepared in advance.

[0045] The cylinder liner 2B is formed of an aluminum alloy pipe cut out so as have a predetermined length and an inner diameter which is slightly smaller than the diameter of the cylinder bore 10 of the finished cylinder 1 (see FIGS. 4 and 5) and provided with two pairs of scavenging ports 16 and 17, two pairs of scavenging inlet openings 21 and 22, the suction port 11 (the inner end portion 11 a thereof), and the exhaust port 12 (the inner end portion 12 a thereof), all of these openings and ports being formed at predetermined locations by means of suitable mechanical working. Additionally, the cylinder liner 2B is provided near the upper end thereof with an annular groove 36 in which the main body 2A of the cylinder is adapted to be fitted.

[0046] The bore-core die 50 is formed of an uncollapsible ordinary core die which is adapted to be employed in a high pressure die casting method, and comprises a columnar portion 52 on which the cylinder liner 2B is externally fitted, a combustion chamber-forming portion 53 which is formed contiguous with the upper portion of the columnar portion 52 and configured to correspond with the combustion chamber 4 of the cylinder 1, and a proximal end portion 54 which is formed contiguous with the lower end of the columnar portion 52. This proximal end portion 54 is connected integrally with the paired scavenging passage-forming portions 55 (56) corresponding in configuration with the scavenging ducts 14 and 15, respectively. A lower half portion of the cylinder liner 2B is designed to be fitted in a gap portion 59 formed between the columnar portion 52 and the paired scavenging passage-forming portions 55 and 56.

[0047] In this case, since the bore-core die 50 and the paired scavenging passage-forming portions 55 and 56 are not intruded into the scavenging ports 16 and 17 (i.e. under-cut portions), the bore-core die 50 and the paired scavenging passage-forming portions 55 and 56 are permitted to withdraw downward out of the cylinder 1 after finishing the cast molding.

[0048] As shown in FIGS. 1 and 2, the cylinder liner 2B is set at first in the bore-core die 50 and the paired scavenging passage-forming portions 55 and 56, and then, the core 46 for suction port and the core 47 for exhaust port are set in place as shown in FIGS. 4 and 5. Thereafter, the metal mold casting is performed by means of high pressure die casting method.

[0049] In this embodiment, prior to setting the cylinder liner 2B in the bore-core die 50, melt intrusion prevention means is provided for preventing melt from entering into the scavenging ports 16 and 17 on the occasion of metal mold casting. Namely, as shown in FIGS. 6 and 7, two pairs of blocking members 31 and 32 each having a U-shaped cross-section are detachably mounted in the scavenging ports 16 and 17, respectively, by introducing them from the outer peripheral surface side of the cylinder liner 2B. These blocking members 31 and 32 are respectively made from an aluminum alloy plate and configured to have the same external size as the size of the scavenging ports 16 and 17. Further, these blocking members 31 and 32 are elastically press-contacted with the inner surface of the scavenging ports 16 and 17, respectively. Further, these blocking members 31 and 32 are also designed such that a step portion is not permitted to generate between the scavenging ports 16 and 17 and the scavenging ducts 14 and 15 of the main body 2A of cylinder.

[0050] Because the outer periphery of each of the scavenging inlet openings 21 and 22 is in close contact with the scavenging passage-forming portions 55 and 56, there is no possibility of the melt entering into the scavenging inlet openings 21 and 22, so that the melt intrusion prevention means described above is not required to be provided at these openings. Further, the suction port 11 as well as the exhaust port 12 are also partially intruded and closed by the core 46 for suction port (a distal end portion 46 a thereof) and by the core 47 for exhaust port (a distal end portion 47 a thereof), the melt intrusion prevention means is not required to be provided at these ports. A plug die 51 having a suitable configuration for forming an ignition plug-mounting hole 28 can be also provided in the casting.

[0051] As described above, after all of these dies have been set in, the insert core 30 is set in the cylinder liner 2B and an outer mold (not shown) is positioned on the outside of the cylinder liner 2B, the die casting is performed by means of the high pressure die casting to obtain a raw cylinder body 1 as shown in FIGS. 4 and 5. Thereafter, the bore-core die 50, the scavenging passage-forming portions 55 and 56, the core 46 for suction port and the core 47 for exhaust port are pulled away, and then, the blocking members 31 and 32 as well as the plug die 51 are removed therefrom. Subsequently, the inner peripheral surface of the cylinder liner 2B is subjected to boring and then, the resultant cylinder body is subjected to predetermined finish treatments such as the formation of the internal thread portion 23 a, thereby obtaining a finished product of the cylinder 1 as shown in FIGS. 11 and 12.

[0052] According to the method of manufacturing a cylinder for an internal combustion engine which is constructed as described in this embodiment, due to the employment of the die and the insert core both being uncollapsible, it is possible to utilize a high-pressure die casting method which enables one to obtain a cast article of high dimensional precision at low cost. Additionally, since the cylinder liner 2B is provided in advance with the scavenging ports 16 and 17, the suction port 11 and the exhaust port 12, it is possible to manufacture the cylinder with higher precision and at lower cost as compared with the conventional manufacturing methods such as the method wherein the port portions such as the scavenging port are cut out by mechanical working after die casting or the method wherein an insert core to be inserted into the scavenging port portion is used. At the same time, it is now possible to obviate the aforementioned problems of the deterioration of heat conductivity as well as the deformation or peeling of these port portions due to the remnant of the insert core in the cast article (cylinder).

[0053] Additionally, since the cylinder liner 2B is formed by making use of an aluminum alloy pipe, the cylinder liner can be manufactured at a lower cost as compared with the case where a liner produced through casting is employed. Further, since the cylinder liner 2B is formed of the same material (aluminum alloy) as that of the main body 2A of the cylinder, there is no possibility of generating any difference in thermal expansion coefficient as well as in thermal conductivity, thereby making it possible to inhibit the generation of problems such as peeling between them, a step portion around the opening such as scavenging port or misalignment between them. Further, since the cylinder liner and the main body of the cylinder are formed of the same material with each other, it is advantageous in terms of recycle (re-use) of materials.

[0054] Furthermore, since the cylinder liner 2B is provided in advance with these scavenging port portions 16 and 17, suction port portion 11 and exhaust port portion 12, there is little possibility of generating relative misalignment among these port portions, thus uniquely determining the positions of the scavenging ports 16 and 17, the suction port 11 and the exhaust port 12, thereby making it possible to provide a cylinder with excellent dimensional precision and preventing the generation of relative mismatching among the scavenging ports 16 and 17, the suction port 11 and the exhaust port 12 with regard to the timing of opening and closing to be effected by the piston.

[0055] Since the melt intrusion prevention means (blocking members 31, 32 and 35) are provided for preventing melt from entering into the scavenging ports 16 and 17 on the occasion of metal mold casting, it is now possible to reliably prevent the melt from entering into the scavenging ports 16 and 17, thus making it possible to save the time and labor required for the finish working of the cylinder such as deflashing work after the casting thereof. Moreover, since the melt intrusion prevention means is designed so as to prevent the generation of a step portion between the scavenging ports 16 and 17 and the scavenging ducts 14 and 15 of the main body 2A of cylinder, it is possible to prevent the generation of turbulence in the scavenging gas flow to be injected in the combustion chamber 4 disposed over the top of piston 60.

[0056] Further, when the inner peripheral edge portion (the inner peripheral edge portion of the scavenging port 16 is represented by reference number 16 a in FIG. 6) of the opening such as the scavenging ports 16 and 17, etc. that has been formed in advance in the cylinder liner 2B is preliminarily chamfered, finish chamfering work after casting can be easily performed.

[0057] Further, as shown in FIG. 10, when a specific region in the outer peripheral surface of the cylinder liner 2B, which is designed to be contacted with the main body 2A of the cylinder is coated (a covering layer 70 which can be formed through electroplating, nonelectrolytic plating, ion plating, etc.) with a metal (for example, zinc, tin, etc.) having a lower melting point than that of the aluminum alloy, the covering layer 70 thus coated is enabled to melt on the occasion of casting, resulting in enhancement of adhesion between the cylinder liner 2B and the main body 2A of the cylinder. As a result, the heat conduction from the cylinder liner 2B to the main body 2A of the cylinder can be enhanced, thus improving the heat dissipation and cooling properties of the cylinder.

[0058] While in the foregoing one embodiment of the present invention has been explained in details for the purpose of illustration, it will be understood that the construction of the device can be varied without departing from the spirit and scope of the invention as claimed in the following claims.

[0059] For example, according to the aforementioned embodiment, two pairs of blocking members 31 and 32 are detachably mounted in the scavenging ports 16 and 17, respectively, as melt intrusion prevention means for preventing the melt from entering into the scavenging ports 16 and 17 on the occasion of metal mold casting. However, such melt intrusion prevention means may be replaced by the following structure for example. Namely, as shown in FIGS. 8 and 9, as melt intrusion prevention means, a thick-walled portion or a rib portion 35 for enabling it to face-contact with each of the cores 55 and 56 for scavenging duct may be provided around a peripheral edge portion excluding the lower skirt portion of the scavenging ports 16 and 17 on the outer peripheral surface of the cylinder liner 2B in such a manner as to prevent the generation of a step portion relative to the scavenging ports 16 and 17.

[0060] As would be clear from the foregoing explanation, in the method of manufacturing a cylinder for an internal combustion engine according to the present invention, due to the employment of the die and the insert core both being uncollapsible, it is now possible to utilize a high-pressure die casting method which enables to obtain a cast article of high dimensional precision at low cost. Additionally, since the cylinder liner is provided in advance with a scavenging port, a suction port and an exhaust port, it is possible to manufacture the cylinder with higher precision and at lower cost as compared with the conventional manufacturing methods such as the method wherein the port portions such as the scavenging port are cut out by mechanical working after die casting or the method wherein an insert core to be inserted into the scavenging port portion is used. At the same time, it is now possible to obviate the aforementioned problems of the deterioration of heat conductivity as well as the deformation or peeling of these port portions due to the remnant of the insert core in the cast article (cylinder).

[0061] Additionally, since the cylinder liner is formed by making use of an aluminum alloy pipe, the cylinder liner can be manufactured at a lower cost as compared with the case where a liner produced through casting is employed. Further, since the cylinder liner is formed of the same material (aluminum alloy) as that of the main body of the cylinder, there is no possibility of generating any difference in thermal expansion coefficient as well as in thermal conductivity, thereby making it possible to inhibit the generation of troubles such as peeling between them, a step portion around the opening such as scavenging port or misalignment between them. Further, since the cylinder liner and the main body of the cylinder are formed of the same material with each other, it is advantageous in terms of recycle (re-use) of materials.

[0062] Furthermore, since the cylinder liner is provided in advance with these scavenging port portion, suction port portion and exhaust port portion, there is little possibility of generating relative misalignment among these port portions, thus uniquely determining the positions of the scavenging port, the suction port and the exhaust port, thereby making it possible to obtain a cylinder of excellent dimensional precision and preventing the generation of relative mismatching among the scavenging port, the suction port and the exhaust port with regard to the timing of opening and closing to be effected by the piston.

[0063] Since the melt intrusion prevention means is provided for preventing melt from entering into the scavenging port on the occasion of metal mold casting, it is now possible to reliably prevent the melt from entering into the scavenging port, thus making it possible to save the time and labor required for the finish working of the cylinder such as deflashing work after the casting thereof. Moreover, since the melt intrusion prevention means is designed so as to prevent the generation of a step portion between the scavenging port and the scavenging duct of the main body of cylinder, it is possible to prevent the generation of turbulence in the scavenging gas flow to be injected in the combustion chamber disposed over the top of piston.

[0064] Further, when the inner peripheral edge portion of the opening such as the scavenging port etc. that has been formed in advance in the cylinder liner is preliminarily chamfered, finish chamfering work after casting can be easily performed.

[0065] Further, when a specific region in the outer peripheral surface of the cylinder liner, which designed to be contacted with the main body of the cylinder, is coated (through electroplating, nonelectrolytic plating, ion plating, etc.) with a metal (for example, zinc, tin, etc.) having a lower melting point than that of the aluminum alloy, the metal thus coated is enabled to melt on the occasion of casting, resulting in enhancement in adhesion between the cylinder liner and the main body of the cylinder. As a result, the heat conduction from the cylinder liner to the main body of the cylinder can be enhanced, thus improving the heat dissipation and cooling properties of the cylinder. 

What is claimed is:
 1. A manufacturing method of a cylinder for an internal combustion engine provided with an inner wall-attached hollow scavenging duct having a scavenging port to be opened and closed by the movement of a piston, the method comprising the steps of: preparing a cylinder liner made of an aluminum alloy pipe and provided with the scavenging port, and a bore-core die as well as a core for scavenging duct both being uncollapsible and configured so as not to intrude into the scavenging port; setting the cylinder liner in place in the bore-core die; and casting, by means of a metal mold casting method, an aluminum alloy as a raw material onto the outer peripheral surface of the cylinder liner to thereby mold a main body of the cylinder.
 2. The manufacturing method according to claim 1, wherein said cylinder liner is provided in advance with a suction port as well as an exhaust port in addition to the scavenging port.
 3. The manufacturing method according to claim 1, which further comprises a step of providing melt intrusion prevention means for preventing melt from entering into the scavenging port on the occasion of metal mold casting.
 4. The manufacturing method according to claim 3, wherein said melt intrusion prevention means is configured so as to prevent the generation of a step portion between the scavenging port and the scavenging duct of the main body of the cylinder.
 5. The manufacturing method according to claim 3, wherein said melt intrusion prevention means comprises a blocking member removably attached to the scavenging port.
 6. The manufacturing method according to claim 3, wherein said melt intrusion prevention means comprises a thick-walled portion or a rib portion configured to be in contact with the core for the scavenging duct and disposed all around an outer periphery of the cylinder liner excluding a lower side of the scavenging port in a manner to prevent the generation of a step portion relative to the scavenging port.
 7. The manufacturing method according to claim 1, wherein a chamfered portion is formed in advance on an inner periphery of an opening such as the scavenging port formed in the cylinder liner.
 8. The manufacturing method according to claim 1, wherein a portion of the outer peripheral surface of the cylinder liner, which contacts with the main body of the cylinder, is coated in advance with a metal having a lower melting point than that of the aluminum alloy.
 9. The manufacturing method according to claim 1 further comprising preventing the generation of a step portion between the scavenging port and the scavenging duct of the main body of the cylinder.
 10. A cylinder for an internal combustion engine provided with an inner wall-attached hollow scavenging duct having a scavenging port to be opened and closed by the movement of a piston, the cylinder being manufactured by the steps of: preparing a cylinder liner made of an aluminum alloy pipe and provided with the scavenging port, and a bore-core die as well as a core for scavenging duct-both being uncollapsible and configured so as not to intrude into the scavenging port; setting the cylinder liner in place in the bore-core die; and casting, by means of a metal mold casting method, an aluminum alloy as a raw material onto the outer peripheral surface of the cylinder liner to thereby mold a main body of the cylinder.
 11. The cylinder according to claim 10, wherein in the manufacturing of the cylinder, said cylinder liner is provided in advance with a suction port as well as an exhaust port in addition to the scavenging port.
 12. The cylinder according to claim 10, wherein the manufacturing of the cylinder further comprises a step of providing melt intrusion prevention means for preventing melt from entering into the scavenging port on the occasion of metal mold casting.
 13. The cylinder according to claim 12, wherein said melt intrusion prevention means in manufacturing the cylinder is configured so as to prevent the generation of a step portion between the scavenging port and the scavenging duct of the main body of the cylinder.
 14. The cylinder according to claim 12, wherein said melt intrusion prevention means in manufacturing the cylinder comprises a blocking member removably attached to the scavenging port.
 15. The cylinder according to claim 12, wherein said melt intrusion prevention means in manufacturing the cylinder comprises a thick-walled portion or a rib portion configured to be in contact with the core for the scavenging duct and disposed all around an outer periphery of the cylinder liner excluding a lower side of the scavenging port in a manner to prevent the generation of a step portion relative to the scavenging port.
 16. The cylinder according to claim 10, wherein in manufacturing the cylinder, a chamfered portion is formed in advance on an inner periphery of an opening such as the scavenging port formed in the cylinder liner.
 17. The cylinder according to claim 10, wherein a portion of the outer peripheral surface of the cylinder liner, which contacts with the main body of the cylinder, is coated in advance with a metal having a lower melting point than that of the aluminum alloy.
 18. The cylinder according to claim 10, wherein the manufacturing of the cylinder further comprises preventing the generation of a step portion between the scavenging port and the scavenging duct of the main body of the cylinder. 